1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the base concentration of a photographic film, such as a negative film, read out with a film scanner.
2. Description of the Related Art
It is essential for printing color images recorded on a negative film onto a sheet of photosensitive with higher quality of colors, photographic printing paper to absorb and eliminate any changes in the concentration, which are caused by a difference between scanners or the effect of deterioration with time, from the color image data read out from the film with a film scanner which also depends on the intrinsic characteristics of its input and output systems. For the purpose, the base concentration value of the film is measured and subtracted from the color image data. For example, the base concentration value in both the R (red) and B (blue) colors are adjusted to be equal to the base concentration value in the G (green) color. There have hence been developed some methods for calculating the base concentration value from the concentration in transparent area of a film which include the intervals between frames and the upper and lower margins, such as disclosed in Japanese Unexamined Patent Publication No. 1997-34024 and 1998-186541.
However, none of the conventional methods for determining the base concentration from the concentration in the intervals between frames and in the upper and lower margins are successful to detect the concentration at a desired accuracy in case that the intervals between frames are scarcely provided or a difference in the concentration between over-scenes is highly significant.